The invention concerns a vehicle lamp, in particular a side marking lamp, as set forth in the classifying portion of claim 1.
The photometric requirements in respect of side marking lamps of motor vehicles are laid down in national and international regulations and requirements. They specify inter alia the angular regions from which and the light intensity with which the light signal must be visible to other road users.
In the case of side marking lamps as are used for example on commercial vehicles such as buses and heavy goods vehicles, the minimum requirements in terms of the visibility range are prescribed for example at 10° upwardly and downwardly respectively and 45° towards the left and the right respectively from a reference axis HV (center line extending in the direction of radiation) of the lamp. In that respect a uniform minimum light intensity is required in the entire visibility range. It is only at the center of light distribution that the light intensity must be markedly higher.
FIG. 1 shows the minimum photometric requirements for a side marking lamp. The window illustrated represents the minimum visibility range of the side marking lamp, with a radiation angle, in relation to a center point 5, of 10° upwardly and downwardly, as indicated at 10° U and 10° D, and 45° towards the left and the right, as indicated at 45° L, 45° R. In that respect, a substantially higher level of light intensity of for example 4 cd is prescribed at the center point 5 (central peak) than in the region 4 (for example 0.6 cd).
When using LEDs as the light source, satisfying that requirement gives rise to problems as an LED has an irregular, approximately bell-shaped radiation characteristic, with a light intensity which is very high at the center 5 and which falls off outwardly in a bell configuration. In the transitional region between the center 5 and the outer region 4 however the light intensity is generally substantially higher than it would have to be in accordance with the minimum requirements. Therefore, to save on light power, light-refracting optical systems are used, which produce a substantially uniformly bright light bar. Such a lamp however can be positioned only in one installation position, for example horizontally.
Known lamps which can be mounted in different positions (for example also turned through 90°) include an optical system which for example produces a circular projection, as is illustrated in FIG. 2 by reference numeral 1. By virtue of that arrangement, it is admittedly possible for the lamp to be fitted in different positions (in turned relationship), but a high level of light power is required in order to appropriately illuminate the respective projection surface.
That is relatively expensive in the case of an LED as additional light power when using LEDs causes a considerable increase in costs, in comparison with incandescent lamps.